The art of printing images with inkjet technology is relatively well known. In general, an image is produced by emitting ink drops from an inkjet printhead at precise moments such that they impact a print medium at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium and emit ink drops at such times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.
Conventionally, a thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a nozzle or orifice plate attached to the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heaters fabricated by deposition, masking and etching techniques on a substrate such as silicon. One or more ink vias cut or etched through a thickness of the silicon serve to fluidly connect the supply of ink to the individual heaters.
To print or emit a single drop of ink, an individual resistive heater is uniquely addressed with a small amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local ink chamber (between the heater and nozzle plate) and be ejected through and projected by the nozzle plate towards the print medium.
In the past, manufacturers typically configured their heater chips with a centrally disposed elongate ink via(s) with attendant heaters on both sides thereof. Recently, as heater chips have become smaller and more densely packed with heaters, some ink vias have only had heaters disposed along a single side thereof. Such designs, however, have maintained their ink via(s) in a central disposition which leads to chip silicon waste. For example, consider the heater chip 725 of FIG. 7A with a single elongate ink via 732, centrally disposed (+), such that about 1000 microns of silicon (in a direction transverse to the elongate extent of the ink via) exist on both sides thereof. If the heater chip has columnar-disposed bond pads 728 near chip edges that parallel heater columns 734-L, 734-R on both sides of the ink via, the chip has fixed distances d1, d2 between the heater columns and bond pads. To wipe the nozzles above the heaters during printhead maintenance routines, a wiper (not shown) sweeps across a surface of the nozzles but, for printhead longevity reasons, does not sweep across the bond pads. Thus, since printers have wipers mechanically and electrically connected to motors and other structures in a manner such that the wipers have fixed times of lowering, raising and traveling, the printheads, in turn, require distances d1, d2 to have some minimum length to effectively wipe the nozzles while avoiding the bond pads.
Now consider the heater chip of FIG. 7B having eliminated the right columnar heaters shown in FIG. 7A, perhaps by more densely packing heaters into column 732-L. If the ink via 732 remains centrally disposed (+) on the chip, wasted silicon space results because wiping is no longer required to the right of the ink via (and no minimum distance is required) yet the distance from the center of the via to the chip periphery 741 remains the same. Keep in mind, the chips 725 of FIGS. 7A, 7B have been greatly simplified and often include additional ink vias and heaters.
Accordingly, the inkjet printhead arts desire heater chips having optimally arranged ink via(s) that minimize silicon costs.